Conventionally, there have been proposed stent delivery systems to indwell a stent at a stenosis or occlusion formed in a living body lumen or body cavity such as blood vessel, bile duct, esophagus, trachea, urethra, digestive tract, and other organs to secure the lumen or body cavity space.
In the above-described stent delivery system, there are both a balloon-expandable stent and a self-expandable stent that can be used depending on the functions and the indwelling method.
In the balloon-expandable stent, the stent itself does not have the expansion function. To indwell the stent at a target part, for example, the stent, mounted on a balloon, is inserted into the target part and thereafter the balloon is inflated to expand (plastically deform) the stent by the inflation force of the balloon. This causes the stent to be brought into tight contact with the inner surface of the target part and fixed.
This type of stent needs the above-described stent dilation operation performed by the balloon. However, since it is possible to indwell the stent by attaching the stent directly to the deflated balloon, there is no large problem regarding the indwelling.
In contrast, in the self-expandable stent, the stent itself has the contraction and expansion function. To indwell this stent at a target part, the stent is inserted into the target part in the contracted state and, thereafter, the stress applied to keep the contracted (or compressed) state is removed. For example, the contracted stent is housed in a sheath having an outer diameter smaller than the inner diameter of the target part and the distal end of this sheath is made to reach the target part. Thereafter, the stent is pushed out from the sheath. The stress load is removed from the stent when it is pushed out due to the release from the sheath, and the stent is thereby expanded and restored to the shape before the contraction. This causes the stent to be brought into tight contact with the inner surface of the target part and fixed.
This type of stent does not need an expansion operation like that for the balloon-expandable stent because the stent itself has the expansion force. In addition, it is free from the problem of the diameter of the stent gradually becoming smaller due to the pressure of a blood vessel or the like and a restenosis thus occurring.
However, the self-expandable stent is generally thought to be more difficult to accurately indwell at the target part than the balloon-expandable stent. This is because, in the balloon-expandable stent, a liquid is merely injected into the balloon after the stent is disposed at the target stenosis. Therefore, the stent does not move forward or backward in the expansion of the stent. On the other hand, in the structure of the delivery system for the self-expandable stent, the stent is housed and restrained between an inner tube and an outer tube and a locking part to restrict the movement of the stent is provided on the stent proximal side of the inner tube. By pulling the outer tube toward the proximal side, the restraint of the stent is released to make the stent be self-expanded. The stent readily moves forward when being expanded which is believed to be due to looseness of the outer tube within the body cavity, or friction between the outer tube and the body cavity or the catheter into which the outer tube is introduced, or friction between the outer tube and a valve of a device called an introducer for introducing the system into the body.
An example of a self-expandable stent delivery system is shown in U.S. Pat. No. 7,815,669 (Japanese Laid-Open Patent No. 2007-97620.
This stent delivery system 1 includes a distal-side tube 2 having a guidewire lumen 21, a proximal-side tube 4 fixed to the proximal portion of the distal-side tube 2, a stent housing tubular member 5 that envelops the distal side of the distal-side tube 2 and is slidable in the proximal direction, a stent 3 housed in the tubular member 5, and a pulling wire 6 for moving the tubular member 5 toward the proximal side. The distal-side tube 2 has a proximal-side opening 23 opened on the proximal side of the distal-side tube 2, a stent locking part 22 that restricts the movement of the stent toward the proximal side, and an operation section including a pulling wire winding-up mechanism and a mechanism to restrict the amount of wire winding-up.
Furthermore, this stent delivery system 1 includes an intermediate tube 7 that encloses the proximal side of the distal-side tube 2 and the proximal side of the stent housing tubular member 5 and that is fixed to the proximal portion of the distal-side tube 2 and the distal portion of the proximal-side tube 4 at its proximal part. The intermediate tube 7 encloses the proximal side of the distal side tube 2 and the proximal side of the stent housing tubular member 5 without restricting the movement of the stent housing tubular member 5 toward the proximal side. One end of the pulling wire 6 is fixed to the stent housing tubular member 5 in the intermediate tube 7. The pulling wire 6 passes between the intermediate tube 7 and the distal-side tube 2 and extends into the proximal-side tube 4.
In this stent delivery system, the proximal-side opening of the guidewire lumen exists not at the proximal end of the system (operation section) but at the proximal end of the distal-side tube. Therefore, in a stent indwelling operation, the operation of exchanging from one delivery system to another stent delivery system is easy. Furthermore, the stent can be discharged by pulling the pulling wire toward the proximal side. Thus, the positional movement of the stent in the stent discharge operation is extremely little.
Although the system of U.S. Pat. No. 7,815,669 is sufficiently effective, it is preferable that the stent discharge operation be easier. In the system of U.S. Pat. No. 7,815,669, the compressed self-expandable stent is in contact with the inner surface of the stent housing tubular member across substantially the entirety of its outer surface. Therefore, in the stent discharge operation, substantially the entire outer surface of the compressed self-expandable stent is in sliding contact with the inner surface of the stent housing tubular member.
Accordingly, it would be desirable to decrease the contact area between the outer surface of the compressed self-expandable stent and the inner surface of the tube body that houses the stent and thereby reduce the sliding contact resistance between the outer surface of the compressed self-expandable stent and the stent housing tube body in the stent discharge operation, to thereby provide a stent delivery system in which the stent discharge operation is made easier.